/a-klə-ˈmā-shən, -ˌklī-/
Noun
1. In English-speaking countries other than the US, is the process in which an individual organism adjusting to a gradual change in its environment (such as a change in temperature, humidity, photoperiod, or pH), allowing it to maintain performance across a range of environmental conditions. (wikipedia.org)
2. Adaptation to a new climate (a new temperature or altitude or environment). (biology-online.org)
3. To accustom or become accustomed to a new climate or environment; adapt. (Dictionary.com)
4. The adaptation of an organism to its natural climatic environment. (wiktionary.org)
Also called acclimatization